U.S. Pat. No. 4,846,300, hereby incorporated by reference, discloses a marine engine with a multi-section injection-molded thermoplastic air box directing air to the fuel system's air intake throat and silencing engine noise emitted back through the throat. The air box has a cover section and a base section mounted to each other solely by a seal along a peripheral seam around the entire perimeter thereof, to prevent fuel leaks. The housing sections are preassembled to each other prior to mounting to the air intake throat. A removeable plug in the cover section allows access through the cover section to bolts mounting the base section to the throat. Access is also enabled to a fuel adjustment screw to enable adjustment, with the air box fully assembled and mounted in place on the throat, to enable adjustment under actual operating conditions. Air guide passages and an air plenum chamber are all molded in place.
U.S. Pat. No. 5,083,538, hereby incorporated by reference, discloses an air intake system for an internal combustion engine associated with the power head of an outboard marine propulsion system. The engine includes a vertical crank shaft and a flywheel mounted to the crank shaft above the engine block. An air manifold is mounted to the forward side of the engine, and includes an air inlet for receiving intake air. The air intake system includes an air flow path or duct defined by a series of walls, a rearwardly facing air intake opening, and a discharge opening for supplying intake air to the air manifold inlet. The engine is enclosed within a cowl assembly, and the air intake opening is located toward the upper end of the cowl assembly interior. The walls defining the air flow duct are formed integrally with a flywheel cover for facilitating assembly of the air flow duct to the engine. The air flow duct minimizes ingestion of water into the engine and reduces engine noise in the boat.
U.S. Pat. No. 9,359,981, hereby incorporated by reference, discloses an outboard motor including a system for enhancement of a first subset of sounds having a desired frequency, and a method for modifying sounds produced by an air intake system for an internal combustion engine powering the outboard motor. The method includes collecting sounds emitted in an area proximate a throttle body of the engine. A first subset of the collected sounds, which have frequencies within desired frequency range, is then amplified. The amplified first subset of sounds is then transmitted to an area outside a cowl covering the engine.
Unpublished U.S. patent application Ser. No. 15/091,007, filed Apr. 5, 2016, and hereby incorporated by reference, discloses an outboard motor including an internal combustion engine and a cowl covering the engine. An air vent allows intake air into the cowl, an air intake duct routes the intake air from the air vent to the engine, and a throttle body meters flow of the intake air from the air intake duct into the engine. A sound enhancement device is located proximate the throttle body. A sound duct is provided, and has an inlet end located proximate the sound enhancement device and an outlet end located proximate an outer surface of the cowl. The sound enhancement device is tuned to amplify a first subset of sounds having a desired frequency that are emitted from the throttle body, and the sound duct transmits the amplified sounds to an area outside the cowl. A method for modifying sounds produced by an air intake system of an outboard motor is also provided.